1. Field of the Invention
The field of the present invention is systems and methods for controlling the torque of driving wheel for use in a traction control for preventing excessive slipping of the driving wheel.
2. Description of the Prior Art
In a so-called traction control system for preventing the excessive slipping of the driving wheel during starting and speed-increasing of a vehicle, there are conventionally known driving-wheel torque control means of a type in which the throttle opening degree in an internal combustion engine is controlled in a feed-back manner (for example, see Japanese Patent Application Laid-open No 7954/87). With such driving-wheel torque control system, the driving-wheel torque can be controlled so that the amount of slippage of the driving wheel becomes an appropriate value, thereby providing a proper driving force suitable to the frictional coefficient of a road surface and to the operational condition of the vehicle.
In the prior art driving-wheel torque control system, however, the last throttle opening degree or a given value is used as an initial throttle opening degree at the start of the feed-back control of the throttle opening degree. For this reason, there is a time lag until the throttle opening degree becomes a value which provides a desired slippage of the driving wheel, and hence, there is a problem in the transition response.
In addition, in the traction control, the throttle valve is controlled in a feed-back manner at the occurrence of an excessive slipping of the driving wheel to limit the output from the internal combustion engine, and if such excessive slipping has been increased to such a value that it cannot be absorbed only by the control of the throttle valve, the cutting of fuel supply is also used to further limit the output from the internal combustion engine.
In such a case, an initial throttle opening degree at a time point when the processing is returned from the fuel cutting to the feed-back control during the traction control is evaluated from the torque condition for the driving wheels to a time point when a predetermined time is elapsed after entering into the fuel cutting and hence, in some cases, the initial throttle opening degree may be evaluated as a value larger than an actually required initial opening degree because of an error due to the indefinite frictional coefficient of a road surface. In addition, when the road surface frictional coefficient is reduced in the course of after determination of an initial degree of opening of the throttle valve up to the return from the fuel cutting, the initial opening degree at the return from the fuel cutting may be too large in some cases. If the initial degree of opening of the throttle valve becomes too large by such reasons, a disadvantage is encountered that the excessive slipping of the driving wheel at the time point of return from the fuel cutting is too large to cause the reentering into the fuel cutting, so that the entering into and returning from the fuel cutting may be repeated.
In addition, in the prior art driving-wheel torque control system, a gear ratio of a transmission is not taken into consideration in finding a surplus torque required to calculate an effective driving-wheel torque and for this reason, it is impossible to find the surplus torque correctly.
The output torque from the internal combustion engine maye be varied even depending upon the air-fuel ratio in addition to the throttle opening degree and an ignition time, and further, the driving-wheel torque may be varied even depending upon the transmitting efficiency of the transmission, the gear ratio, the hydraulic pressure of a brake and the like in addition to the output torque from the internal combustion engine. Therefore, the prior art driving torque control system has another problem that when the driving wheel torque is desired to be controlled to a predetermined value in a certain operational condition by using a plurality of parameters (e.g., the throttle opening degree and the ignition time) in combination, a close control cannot be conducted unless the total amount of variation in driving wheel torque corresponding to the amount of variation in each parameter is grasped correctly.